Working with your laptop on your legs for too long can cause permanent damage to your skin leading to what doctors term ‘toasted skin syndrome’.

The exposure of your legs to long term heat can cause skin to develop an unusual-looking mottled condition according to medical reports.

A 12-year-old boy, in one recent case, developed a sponge-patterned skin discoloration on his left thigh after playing computer games a few hours every day for several months.

'He recognized that the laptop got hot on the left side; however, regardless of that, he did not change its position,' Swiss researchers wrote in the respected medical journal Pediatrics.

In a separate case, a Virginia law student sought treatment for the mottled discoloration on her leg.

The young woman spent about six hours a day working with her computer propped on her lap. The temperature underneath the laptop registered 125 degrees.

The condition, which is generally harmless, can also can be caused by overuse of heating pads and other heat sources that usually aren't hot enough to cause burns.

This condition can cause skin to permanently darken.